Demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to mobile devices have increased. Accordingly, a great deal of research on batteries that can meet various needs is being carried out.
Particularly, demand for lithium secondary batteries, such as a lithium ion battery or a lithium ion polymer battery having merits of high energy density, high discharge voltage, output stability, or the like is high.
These lithium secondary batteries are charged and discharged while repeating a process of intercalation in which lithium ions are intercalated into a graphite electrode of a negative electrode from a lithium metal oxide of a positive electrode and deintercalation.
In such an electrolyte of lithium second battery, not only lithium ions but also negative ions are moved to form polarization in the battery.
Accordingly, research on a high-concentration electrolyte is being carried out such that when the high-concentration electrolyte having a higher transference number than electrolytes generally used nowadays is used, the battery performance can be improved due to the increase in the amount of ions present in the electrolyte and the accompanying increase in ion conductivity.
Regarding this, patent document 1 discloses a secondary battery electrolyte containing a high-concentration electrolytic salt having an electrolytic salt with a concentration of greater than 1.1 M, preferably, 1.3 M to 1.8 M.
However, since the electrolyte disclosed in patent document 1 above contains only an electrolytic salt with a concentration of greater than 1.1 M and equal to or smaller than 2 M, the increase in ion conductivity is limited, and when the concentration of the electrolytic salt is greater than 2 M, the increases in the viscosity and surface tension of the electrolyte become remarkable, so that the ion conductivity is decreased, and since the wettability of a separator is not good, there is a drawback in that the degradation of battery performance is concerned.
Thus, there are needs to manufacture a non-aqueous electrolyte, by which the improvement of battery performance can be expected by lowering the viscosity and the surface tension of the high-concentration electrolytic salt, and a secondary battery using the electrolyte.